Known to the art are systems for determining the orientation of the wheels of a vehicle, in particular a motor vehicle, which enable an automatic measurement of one or more characteristic angles of the wheels, for example the so-called convergence and camber angles, in order to verify proper alignment of the wheels themselves in a reference system fixed with respect to the vehicle. In a known way, in fact, an incorrect alignment, with respect to the design parameters, can cause an excessive or non-homogeneous wear of the tires, and moreover can cause problems in driveability and stability of the vehicle.
Systems for determining orientation of the wheels of a vehicle are in general configured for detecting, via purposely provided detection devices, the spatial orientation of the plane of each wheel with respect to a single orthonormal triad taken as reference (it should be noted that by “plane of the wheel” is here understood the plane in which an outer lateral surface of the wheel lies, for example the surface identified by the corresponding rim) so as to enable appropriate corrective actions to be undertaken for restoring alignment of the wheels.
In particular, some systems envisage the use of devices for detecting the characteristic angles of the wheels, or in any case of appropriate sensitive elements, directly coupled to the wheels of the vehicle via purposely provided engagement tools (the so-called “clamps”), so as to identify the orientation thereof. In this case, to prevent damage to the detection devices, a considerable care is required in their installation on the wheels and moreover during execution of the measurement steps.
Other systems displace the point of observation to outside the vehicle in such a way as to define a reference system (SdR) fixed with respect to that of the attitude, through observation of the angular variations of the wheels by one or more detection devices (the so-called “measuring heads”) set in a position external to the vehicle and independent of the orientation of the vehicle itself. In this case, the elements that are applied to the wheels of the vehicle may be altogether passive, and hence be advantageously less delicate and sensitive to damage.
In particular, some systems envisage positioning of the detection devices directly on the hydraulic ramp (designed to raise the vehicle under observation, in a known way), in a lateral position with respect to the vehicle. Other systems envisage positioning of the detection devices in a front position with respect to the vehicle itself, on structures that are fixed or can move independently, which are set at a distance and are separate both from the vehicle and from the hydraulic ramp. In the former case, the image-acquisition devices follow the movements of the hydraulic ramp but, for this reason, the deformations thereof must be compensated dynamically. In the latter case, the image-acquisition devices must follow the movements of the hydraulic ramp so as to maintain pointing on the wheels, but do not need to compensate the deformations thereof.
In any case, said systems generally use appropriate targets coupled to the wheels of the vehicle in such a way as to highlight the rotation and position thereof in space. The detection devices include, in particular, appropriate image-acquisition tools, designed to frame the targets coupled to the wheels and acquire images corresponding thereto, on the basis of which appropriate processing operations are carried out to determine the orientation of each wheel and the mutual alignment.
Targets of a known type usually present a two-dimensional configuration with a plane surface represented on which are two-dimensional images of multiple shapes, which can be recognized by a processing device, which is coupled to the detection devices and generally carries out a so-called “best fit” operation between geometries of two-dimensional images identified on a generically plane surface forming part of the real target and the two-dimensional images that the image-acquisition devices supply in their own reference system. This operation enables dynamic determination of the orientation of the target in space, and hence definition of elementary roto-translations corresponding to the linear and angular movement of each wheel within a single reference system (for example, the reference system of the vehicle). Then, said elementary roto-translations, set in appropriate relation with one another, are used for defining further more complex rotations and translations, which regard more specifically the characteristics of attitude and alignment of the vehicle.
In the use of said systems in a workshop, there may arise cases where the simultaneous visibility, for each side of the vehicle, of the target applied to the front wheel and of the target applied to the rear wheel becomes problematical, and at times impossible, owing to the dimensional characteristics of the vehicle itself (which may vary in a wide range where the track may be comprised, for example, between 1000 mm and 1750 mm, and the wheelbase may be comprised, for example, between 1800 mm and 4100 mm), or else can be jeopardized by an incorrect alignment of the vehicle itself with respect to the measuring area defined by the hydraulic ramp. Consequently, alignment systems of a known type, for covering the wide range of existing vehicles completely, requires intervention of the operator, who must displace each detection device along the hydraulic ramp in an appropriate way to adapt to, or follow, the position of the wheels and of the associated targets.
Said operation may prove complicated, also because it requires a manual displacement of the detection devices, with consequent movement of the corresponding wiring. Moreover, the very operation of displacement may cause accidental damage to the detection devices, thus jeopardizing the operations of measurement or giving rise to errors of measurement in the subsequent detection of the angles of interest.
The patent application No. EP 1 887 317 A1 describes a system for measuring the alignment of the wheels of a vehicle, which envisages use, on each side of the vehicle, of four video cameras, designed to frame, in pairs, a respective wheel and the corresponding target, which has a two-dimensional configuration. Processing of the images is of a stereo type, since it is necessary to process jointly two images of one and the same target, taken from different angles (by the two different video cameras of each pair), to determine the angles of alignment thereof with respect to a reference system. Each video camera is individually mobile and can be displaced with respect to a load-bearing structure, in particular along a respective guide. Said solution is clearly complex to manage and use, given that it requires amongst other things maintenance of the correct mutual positioning of a large number of devices for acquiring the images, and moreover involves complex operations of processing of the images themselves.
Other systems for measurement of alignment, albeit using a smaller number of filming elements, require in any case a stereo processing of the images corresponding to the framed planar targets, for measuring the angles of alignment. In order to acquire stereo images of the respective target and enable an operation of measurement of the angles of alignment, each filming element can be individually displaced so as to assume, in consecutive times, at least two different positions with respect to the target itself. Also said systems consequently prove in general complex to produce and use.